In U.S. Pat. No. 4,898,156, entitled "Suture Anchor"; U.S. Pat. No. 4,899,743, entitled "Suture Anchor Installation Tool"; and U.S. Pat. No. 4,968,315, entitled "Suture Anchor and Suture Anchor Installation Tool" (each of which is presently owned by Mitek Surgical Products, Inc., of Norwood, Mass., the assignee of this application), there are disclosed a variety of anchors of the sort adapted to anchor one end of a piece of conventional suture in bone. These patents further disclose several anchor installation tools for deploying the suture anchors therein disclosed. Complete details of the construction and use of these various anchors and anchor installation tools are provided in the specifications and drawings of the above-identified U.S. Patents. Those specifications and drawings are hereby incorporated by reference into the present application.
It, therefore, will be understood that anchoring devices of the type including a coupling member and at least one curved barb extending upwardly and outwardly from an end of the coupling member are known in the art. It also will be understood that tools for deploying such anchoring devices in holes in surfaces of workpieces similarly are known in the art. As the requirements of users of such devices, particularly in the medical field, have become more demanding, however, known anchoring devices and installation tools therefor have encountered problems. Particular among these problems are (1) the possibility of known anchors to fail (i.e., to become dislodged), (2) the diameter of the anchor-receiving hole in the workpiece required for deployment of the anchor, (3) the need for precise location of the barb(s) both during anchor insertion and at final deployment to avoid damage to delicate structures (such as a joint) adjacent to the hole, and (4) in multi-barb configurations, the need for deployment means which assure the central location of the coupling member of the anchor within the anchor-receiving hole during the insertion operation, at least until the engagement of the respective outer barb ends with the sidewall of the hole at substantially equal depths is achieved. The reasons for these problems will become apparent in the following general synopsis of these known anchoring systems.
As noted above, anchors are known which include a coupling member and at least one barb extending upwardly and outwardly from an end of the coupling member. The coupling member generally comprises a piece of 6A14V titanium alloy having a first end surface, a second end surface and a longitudinal axis. The first end surface lies in a plane substantially normal to the longitudinal axis, while the plane of the second surface may be either normal to, or located at an acute angle to, the longitudinal axis. In either alternative, suture attachment means are associated with the second surface. Such attachment means may take several forms. For example, a blind hole may extend centrally into the second surface. The blind hole is adapted to receive a knot formed in one end of the suture. The blind hole also may be connected to the periphery of the coupling member by a slot in order to allow the free end of the suture to extend more easily toward the first end of the coupling member and then out of the hole wherein the anchor is located.
Alternatively, a bore may extend substantially normally into a second surface lying in a plane located at an acute angle to the longitudinal axis. In that case, the bore extends through the coupling member so as to exit at a portion of its sidewall between the first and second ends on the opposite side of the coupling member from that over which the barb extends. A suture may extend through this bore and then substantially directly upwardly toward the open end of the anchor-receiving hole. A knot at the end of the suture threaded through the bore, engaging the second surface, assures the secure connection to the anchor of an object attached to the other end of the suture. In another alternative, the coupling member may define a longitudinal bore therethrough which allows an end of a suture to extend longitudinally through the coupling member for securement to the second surface, for example by the formation of a knot adapted to bear against the second surface adjacent the opening of the bore therein.
As will become apparent below, this tendency in the art of associating the attachment of the suture with the second end of the coupling member can be a source of difficulty to known anchors of the type described. Further, the secure attachment of the object to the workpiece surface with a single suture strand can be difficult. If proper tension is not maintained both during the attachment process and thereafter, the object may move relative to the workpiece, thereby possibly causing damage to adjacent structures.
At least one curved barb extends upwardly and outwardly from the first end of the coupling member in these known anchors. The barb is commonly formed of a length of nickel titanium alloy wire which in its unrestrained state defines an arc having a radius greater than the radius of the coupling member. The barb may be formed integrally with the coupling member, but more commonly one end of the wire extends into a hole in the first surface. In the latter case, the exterior of the coupling member commonly is crimped adjacent to the hole to assure the fixed location of the wire end therein. Also in the latter alternative, at least about 90 degrees of the arc of the barb remains unrestrained by the hole in the first surface of the coupling member. The nickel titanium alloy is chosen such that the barb is capable of being elastically deformed to a substantially straight configuration when desired (i.e., so that the barb's second end can be shifted from its location radially outboard of the sidewall of the coupling member when the free end of the barb is unrestrained to a location in general alignment with the end of the barb engaging the hole in the first end of the coupling member). By way of example, the barb may be made out of binary nitinol such as that sold by Furukawa of Japan and Raychem Corporation of Menlo Park, Calif., or it might be made out of ternary nitinol such as that sold by Raychem Corporation and described in U.S. Pat. No. 4,505,767 (Quinn).
Anchors of the type just described are deployed in holes in the surfaces of workpieces and connected to objects lying on the surface of the workpiece adjacent the hole. Various tools have been developed to accomplish this deployment. In one form, the tool included three mutually telescoping elements; namely, an outer insertion cannula, a suture anchor loader adapted to telescope within the insertion cannula, and a plunger adapted to telescope within the suture anchor loader. The coupling member is inserted into the proximal end of the outer insertion cannula with the unrestrained barb extending out of the proximal end of the outer insertion cannula. Next, the barb is inserted into the distal end of the suture anchor loader, and the loader is telescoped down into its outer insertion cannula. This causes the barb to be deformed into a substantially straight configuration within the central bore of the loader. Next, the plunger is telescoped into the loader until its distal end contacts the proximal end of the deformed barb. Then the distal end of the insertion tool is located within the hole in the workpiece adjacent the desired anchor location. Finally, the plunger is driven towards the distal end of the insertion cannula, so as to drive the anchor out of the insertion tool and into the workpiece at the desired location. See U.S. Pat. No. 4,898,156 identified above.
Subsequently, it was realized that anchor-receiving hole diameters could be reduced by allowing the sidewall of the hole in the workpiece to deform the barb(s) as the anchor is inserted. The outer insertion cannula and plunger, therefore, were deleted, and a longitudinal slot was provided adjacent to the distal end of the anchor loader adapted to permit the barb to extend radially outwardly from the loader when the anchor is inserted into its loading end. The engagement of the barb with the sidewall of the hole allows the anchor loader to be pulled out of the hole in the workpiece, leaving the anchor in place. See U.S. Pat. No. 4,899,743 identified above.
Still later, in response to a desire for improved engagement between the insertion tool and the suture anchor, as well as in response to other desires such as improved suture attachment and workpiece hole diameters, the diameter of the portion of the coupling member adjacent to its first surface was reduced relative to the diameter of the remainder of the coupling member. This construction allows the reduced-diameter portion of the suture anchor to be received within the insertion tool, yet permits the diameter of the anchor loader to be reduced to that of the larger portion of the coupling member. See U.S. Pat. No. 4,968,315.
Certain problems can be encountered with bone anchors of the sort disclosed in U.S. Pat. Nos. 4,898,156; 4,899,743; and 4,968,315, when only one barb is provided and the suture is attached to the second end of the coupling member (i.e., at the end of the coupling member opposite to that which the single barb is attached to), and the second end of the coupling member is disposed at an acute angle relative to the longitudinal axis of the coupling member. For one thing, with such bone anchors, the suture generally extends parallel to, and external of, at least a portion of the bone anchor during insertion into the workpiece. In some circumstances, friction between the workpiece and the coupling member and/or the insertion tool can damage or even sever the suture during insertion. For another thing, in certain types of soft workpieces, e.g. diseased bone, applying a load to the suture attached to the distal end of the suture anchor (i.e., to the angled second end of the coupling member) can cause the suture anchor to pivot in the workpiece, about the proximal end of its barb, thereby possibly becoming dislodged. Furthermore, particularly with suture anchors of the sort disclosed in U.S. Pat. No. 4,968,153, which attach the barb to a reduced diameter first end portion, the provision of multiple barbs can cause the size of the suture anchors to significantly increase, which can be undesirable.